Artificial lipid bilayers formed on solid surface supports are widespread model systems to study physical, chemical, as well as biological aspects of cell membranes and fundamental interfacial interactions. The approach to use a thin polymer film representing a cushion for lipid bilayers prevents incorporated membrane proteins from pinning to the support and mimics the native environment of a lipid bilayer in certain aspects of the extracellular matrix and intracellular structures. A key component for cell anchorage to extracellular fibronectin is the transmembrane adhesion receptor alpha(5)beta(1) integrin. Its transport dynamics and clustering behavior plays a major role in the assembly of focal adhesions, which mediate mechanical forces and biochemical signals of cells with their surrounding. The system investigated herein is envisioned to use extrinsically controlled stimuli-responsive polymer cushions to tune the frictional drag between polymer cushion and mobile membranes with incorporated integrins to actively regulate lipid membrane characteristics. To attain this goal, a temperature- and pH-responsive polymer based on poly(N-isopropylacrylamide) copolymers containing varying amounts of carboxyl-group-terminated comonomers at different aliphatic spacer lengths (PNIPAAm-co-carboxyAAM) was surface-grafted to a poly(glycidyl methacrylate) anchorage layer. The swelling transitions were characterized using atomic force microscopy, ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) and found to be tunable over a wide range of temperature and pH. In agreement with the behavior of the polymers in solution, longer alkyl spacers decreased the phase transition temperature T(P) and higher contents of carboxylic acid terminated comonomers increased T(P) at alkaline conditions and decreased T(P) at acidic conditions. Remarkably, the point where the degree of carboxyl group deprotonation balances the T(P)-lowering effect of the alkyl spacer was distinctive for each alkyl spacer length. These findings illustrate how the local and global balance of hydrophilic and hydrophobic interactions along the copolymer chain allows to adjust the swelling transition to temperatures below, comparable, or above those observed for PNIPAAm homopolymers. Additionally, it could be shown that surface-grafting leads to a decrease in T(P) for PNIPAAm homopolymers (7°C) and copolymers (5°C - 10°C). The main reason is the increase in local polymer concentration of the swollen film constrained by dense surface anchorage in comparison to the behavior of dilute free chains in solution. In accordance with the Flory-Huggins theory, T(P) decreases with increasing concentration up to the critical concentration. Biological functionalization of the PNIPAAm-co-carboxyAAm thin films was demonstrated for the cell adhesion ligand peptide cRGD via carbodiimide chemistry to mimic extracellular binding sites for the cell adhesion receptors integrin. The outcome of QCM-D measurements of cRGD-functionalized surfaces showed a maintained stimuli-responsiveness with slight reduction in T(P). A drying/rehydration procedure of a 9:1 lipid mixture of the cationic lipid dioleoyl-trimethylammoniumpropane (DOTAP) and the zwitterionic dioleoyl-phosphatidylcholine (DOPC) was utilized to form lipid bilayer membranes on PNIPAAm-co-carboxyAAM cushions. Fluorescence recovery after photobleaching (FRAP) revealed that lipid mobility was distinctively higher (6.3 - 9.6) µm2 s-1 in comparison to solid glass support ((3.0 - 5.9) µm2 s-1). In contradiction to the initial expectations, modulation of temperature and pH led to poor variations in lipid mobility that did not correlate with the PNIPAAm cushion swelling state. The results suggested a weak coupling of the lipid bilayer with PNIPAAm polymer cushions that can be slightly tuned by electrostatic interactions. The transmembrane adhesion receptor alpha(5)beta(1) integrin was reconstituted into liposomes consisting of DOPC/sphingomyelin/cholesterol 2:2:1 for the formation of polymer cushioned bilayers. PNIPAAm- co-carboxyAAM and maleic acid (MA) copolymers were used as cushions, both with the option for cRGD functionalization. On the MA copolymer cushions, fusion of proteoliposomes resulted in supported bilayers with mobile lipids as confirmed by FRAP. However, incorporated integrins were immobile. In an attempt to explain this observation, the medium-sized cytoplasmic integrin domain was accounted to hamper the movement by steric interactions with the underlying polymer chains in conjunction with electrostatic interactions of the cationic cytoplasmic domain with the oppositely charged MA copolymer. On the PNIPAAm-co-carboxyAAM cushion only a drying/rehydration procedure lead to bilayer formation. However, again the integrins were immobile, presumably due to the harsh treatment during preparation. Nevertheless, the results of the investigated set of PNIPAAm copolymer films suggest their application as temperature- and pH-responsive switchable layers to control interfacial phenomena in bio-systems at different physiological conditions. The PNIPAAm-co-carboxyAAm cushioned bilayer system represents a promising step towards extrinsically controlled membrane – substrate interactions.

Artificial lipid bilayers formed on solid surface supports are widespread model systems to study physical, chemical, as well as biological aspects of cell membranes and fundamental interfacial interactions. The approach to use a thin polymer film representing a cushion for lipid bilayers prevents incorporated membrane proteins from pinning to the support and mimics the native environment of a lipid bilayer in certain aspects of the extracellular matrix and intracellular structures. A key component for cell anchorage to extracellular fibronectin is the transmembrane adhesion receptor alpha(5)beta(1) integrin. Its transport dynamics and clustering behavior plays a major role in the assembly of focal adhesions, which mediate mechanical forces and biochemical signals of cells with their surrounding. The system investigated herein is envisioned to use extrinsically controlled stimuli-responsive polymer cushions to tune the frictional drag between polymer cushion and mobile membranes with incorporated integrins to actively regulate lipid membrane characteristics. To attain this goal, a temperature- and pH-responsive polymer based on poly(N-isopropylacrylamide) copolymers containing varying amounts of carboxyl-group-terminated comonomers at different aliphatic spacer lengths (PNIPAAm-co-carboxyAAM) was surface-grafted to a poly(glycidyl methacrylate) anchorage layer. The swelling transitions were characterized using atomic force microscopy, ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) and found to be tunable over a wide range of temperature and pH. In agreement with the behavior of the polymers in solution, longer alkyl spacers decreased the phase transition temperature T(P) and higher contents of carboxylic acid terminated comonomers increased T(P) at alkaline conditions and decreased T(P) at acidic conditions. Remarkably, the point where the degree of carboxyl group deprotonation balances the T(P)-lowering effect of the alkyl spacer was distinctive for each alkyl spacer length. These findings illustrate how the local and global balance of hydrophilic and hydrophobic interactions along the copolymer chain allows to adjust the swelling transition to temperatures below, comparable, or above those observed for PNIPAAm homopolymers. Additionally, it could be shown that surface-grafting leads to a decrease in T(P) for PNIPAAm homopolymers (7°C) and copolymers (5°C - 10°C). The main reason is the increase in local polymer concentration of the swollen film constrained by dense surface anchorage in comparison to the behavior of dilute free chains in solution. In accordance with the Flory-Huggins theory, T(P) decreases with increasing concentration up to the critical concentration. Biological functionalization of the PNIPAAm-co-carboxyAAm thin films was demonstrated for the cell adhesion ligand peptide cRGD via carbodiimide chemistry to mimic extracellular binding sites for the cell adhesion receptors integrin. The outcome of QCM-D measurements of cRGD-functionalized surfaces showed a maintained stimuli-responsiveness with slight reduction in T(P). A drying/rehydration procedure of a 9:1 lipid mixture of the cationic lipid dioleoyl-trimethylammoniumpropane (DOTAP) and the zwitterionic dioleoyl-phosphatidylcholine (DOPC) was utilized to form lipid bilayer membranes on PNIPAAm-co-carboxyAAM cushions. Fluorescence recovery after photobleaching (FRAP) revealed that lipid mobility was distinctively higher (6.3 - 9.6) µm2 s-1 in comparison to solid glass support ((3.0 - 5.9) µm2 s-1). In contradiction to the initial expectations, modulation of temperature and pH led to poor variations in lipid mobility that did not correlate with the PNIPAAm cushion swelling state. The results suggested a weak coupling of the lipid bilayer with PNIPAAm polymer cushions that can be slightly tuned by electrostatic interactions. The transmembrane adhesion receptor alpha(5)beta(1) integrin was reconstituted into liposomes consisting of DOPC/sphingomyelin/cholesterol 2:2:1 for the formation of polymer cushioned bilayers. PNIPAAm- co-carboxyAAM and maleic acid (MA) copolymers were used as cushions, both with the option for cRGD functionalization. On the MA copolymer cushions, fusion of proteoliposomes resulted in supported bilayers with mobile lipids as confirmed by FRAP. However, incorporated integrins were immobile. In an attempt to explain this observation, the medium-sized cytoplasmic integrin domain was accounted to hamper the movement by steric interactions with the underlying polymer chains in conjunction with electrostatic interactions of the cationic cytoplasmic domain with the oppositely charged MA copolymer. On the PNIPAAm-co-carboxyAAM cushion only a drying/rehydration procedure lead to bilayer formation. However, again the integrins were immobile, presumably due to the harsh treatment during preparation. Nevertheless, the results of the investigated set of PNIPAAm copolymer films suggest their application as temperature- and pH-responsive switchable layers to control interfacial phenomena in bio-systems at different physiological conditions. The PNIPAAm-co-carboxyAAm cushioned bilayer system represents a promising step towards extrinsically controlled membrane – substrate interactions.

The objective of this thesis was to advance understanding in the field of biolubrication, finding inspiration from the human synovial joints. This was addressed by investigating the association of key biolubricants and the resulting lubrication performance. Techniques employed during the course of this work were Atomic force microscopy (AFM), Quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray reflectivity (XRR). Key synovial fluid and cartilage components like dipalmitoylphosphatidylcholine (DPPC), hyaluronan (HA), lubricin, and cartilage oligomeric matrix protein (COMP) have been used in the investigations. Focus was towards two lubrication couples; DPPC-hyaluronan and COMP-lubricin. DPPC-hyaluronan mixtures were probed on hydrophilic silica surfaces and COMP-lubricin association structures were explored on weakly hydrophobic poly (methyl methacrylate) (PMMA) surfaces. Investigations of the COMP-lubricin pair revealed that individually these components are unable to reach desired lubrication. However in combination, COMP facilitates firm attachment of lubricin to the PMMA surface in a favourable confirmation that imparts low friction coefficient. DPPC and hyaluronan combined impart lubrication advantage over lone DPPC bilayers. Hyaluronan provides a reservoir of DPPC on the surface and consequently self-healing ability. Other factors like temperature, presence of calcium ions, molecular weight of hyaluronan, and pressure were also explored. DPPC bilayers at higher temperature had higher load bearing capacity. Association between DPPC Langmuir layers and hyaluronan was enhanced in the presence of calcium ions, and lower molecular weight hyaluronan had a stronger tendency to bind to DPPC. At high pressures, DPPC-hyaluronan layers were more stable compared to lone DPPC bilayers. / <p>QC 20170210</p>

El conocimiento de las interacciones entre célula/proteína/biomaterial es fundamental para la ingeniería de superficies debido a las numerosas aplicaciones biomédicas y biotecnológicas que se están desarrollando así como al éxito clínico que han alcanzado muchos implantes. La respuesta biológica final inducida por los implantes está fuertemente influenciada por las interacciones superficiales entre los componentes biológicos y el material sintético. Las propiedades físicas y químicas de la superficie de un biomaterial, en lugar de las propiedades en su masa, influyen directamente en la capa de proteínas que se adsorben sobre el biomaterial y, como consecuencia de ello, en la respuesta celular a la misma, tanto in vitro como in vivo.El objetivo de esta tesis doctoral es profundizar en el conocimiento de las interacciones material-biosistema, con el énfasis en el descubrimiento de relaciones entre las propiedades superficiales de las superficies de titanio y su respuesta biológica in vitro.El titanio comercialmente puro (Ti c.p.) está siendo ampliamente utilizado con éxito durante muchos años como biomaterial para implantes en cirugía ósea. Su excelente biocompatibilidad se basa en sus adecuadas propiedades mecánicas y, con mayor importancia, en su excelente resistencia a la corrosión. Esta última se debe principalmente a la formación espontanea de una fina película de óxido de titanio que le confiere protección natural contra los ataques degradativos. La modificación de la topografía de la superficie del titanio ha sido objeto de investigación en el pasado con el fin de mejorar la osteointegración. El granallado de partículas es una de las tecnologías más utilizadas para conferir rugosidad a las superficies del titanio. La rugosidad óptima y el tipo de partículas abrasivas del granallado para una respuesta óptima in vitro e in vivo fue previamente determinada en nuestro laboratorio. Sin embargo, todavía están por determinar cuáles son las causas últimas que llevan al biomaterial a su exitosa respuesta biológica.En este trabajo se han estudiado superficies pulidas y rugosas de Ti c.p. obtenidas mediante el granallado con partículas abrasivas de diferente composición química(Al2O3 y SiC) y diferentes tamaños (212-300&#956;m; 425-600&#956;m; 1000-1400&#956;m). La completa caracterización de las propiedades física y química de la superficie, incluyendo la rugosidad, la composición química, la mojabilidad/energía libre y la carga eléctrica de las superficies ensayadas ha llevado a una serie de relevantes conclusiones. Entre ellas, cabe destacar que a) la composición química de las partículas de granallado, así como el método de esterilización fueron los principales factores que influyeron en la mojabilidad y la energía libre superficial de las superficies de titanio estudiadas, b) el método de esterilización cambió en la energía superficial el carácter de donante de electrones de las superficies mediante el cambio de la cantidad y la naturaleza de las sustancias adsorbidas, y c) la composición química de las partículas de granallado no influyó en la carga eléctrica a pH fisiológico ni en el punto isoeléctrico de las superficies.Un segundo paso consistió en el uso de una microbalanza de cristal de cuarzo con monitorización de la energía de disipación, para el estudio de la cinética de adsorción (cantidad y conformación) y de los procesos de adsorción competitiva de tres proteínas de especial interés en los procesos de curación del hueso - la albúmina de suero bovino (BSA), el fibrinógeno (Fbg), y la fibronectina (Fn)- en sensores lisos recubiertos de TiO2. Se determinaron diferentes modelos de procesos de adsorción con una, dos o múltiples pasos distinguibles en función de las proteínas en solución. La capa adsorbida de BSA mostró los cambios más significativos en sus propiedades mecánicas, de conformación y de incorporación de agua hasta que se alcanzaron las condiciones estables de adsorción de proteínas. La BSA, la más pequeña de las proteínas ensayadas, desplazó la Fn y el Fbg cuando se ensayó en condiciones de la competencia por la adsorción, indicando su mayor afinidad por las superficies de TiO2. También se emplearon técnicas de marcaje fluorescente para el estudio de la adsorción proteica en superficies rugosas granalladas. En este estudio, por un parte, se pudo determinar que la cantidad de Fn y BSA adsorbidas en las superficies granalladas está directamente correlacionada con su energía superficial. Por otra parte, se visualizó la adsorción de fibronectina en solución sobre muestras granalladas rugosas de Ti. La Fn formó un patrón irregular de adsorción con una mayor cantidad de proteína adsorbida en los picos que en los valles de la topografía.También se evaluó la organización espacial de la matriz extracelular de los osteoblastos, ECM, sobre superficies de Ti lisas y rugosas por medio de la visualización de las fibrillas de Fn teñidas con marcador fluorescente. Las células osteoblásticas depositaron las fibrillas de Fn con un determinado patrón organizado dentro de la matriz total secretada. Aparecen como una película que cubre la parte superior de las diferentes superficies rugosas de titanio. Un resultado relevante es que el espesor de esta capa aumentó con la rugosidad de la topografía subyacente. Sin embargo no más de la mitad de la máxima distancia pico-valle se cubrió con la proteína secretada y/o reorganizada.Por último, teniendo en cuenta las diferencias en la organización de la ECM y laadsorción de Fn en las superficies ensayadas de Ti, se realizó un estudio de qRT-PCR para determinar la influencia de las propiedades superficiales del titanio, con y sin preadsorción de Fn, en la respuesta osteoblástica. La expresión génica de la subunidad &#61537;5 de la integrina celular, como marcador de la adhesión celular, se incrementó en las superficies granalladas con SiC en comparación con las granalladas con alúmina. Este resultado fue correlacionado con la mayor cantidad de Fn adsorbida debido a la mayor energía superficial de las superficies granalladas con SiC. El aumento de la rugosidad, así como la presencia de partículas de alúmina en las superficies rugosas incrementó la actividad de ALP y la expresión génica de ALP mRNA por los osteoblastos, y por lo tanto su diferenciación. / The understanding of cell/protein/biomaterial interactions is critical to the engineering of substrates for numerous biomedical and biotechnological applications and to the clinical success of implants. The final biological response induced by implants is strongly influenced by the biological-components/synthetic-material surface interactions. It is well accepted that the physical and chemical surface properties of a biomaterial rather than its bulk properties will influence the protein adlayer and then the cell response to it, both in vitro and in vivo.The aim of this PhD thesis is to gain an increased understanding of the materialbiosystem interactions, with an emphasis on establishing correlations between surface properties of titanium surfaces and its in vitro biological response.Commercially pure titanium (c.p. Ti) is being widely and successfully used implant biomaterial in bone surgery over many years. Its excellent biocompatibility is based in its appropriate mechanical properties and, more importantly, in its excellent corrosion resistance, which is mainly due to the presence of a naturally-occurring thin protective titanium oxide film. Modification of titanium surface topography has been a subject of research in the past with the purpose of improving its osseointegration. Grit blasting is one of the most used technologies to roughen titanium surfaces for this purpose. The optimal roughness and type of abrasive blasting-particles for a better in vitro and in vivo response was previously determined in our lab. However, which and how different relevant surface properties of the blasted titanium surfaces induce that optimal biological behavior is still poorly understood.Smooth/polished and rough c.p. Ti surfaces obtained by blasting with abrasiveparticles of different chemical composition (Al2O3 and SiC) and different sizes (212-300&#956;m; 425-600&#956;m; 1000-1400&#956;m) were studied. The comprehensive characterization of physical and chemical surface properties, including roughness, chemical composition, wettability/free energy and electrical charge of the tested surfaces led to a series of relevant conclusions. Among them, it is worth noting that a) the chemical composition of the grit-blasting particles as well as the method of sterilization were found the main factors influencing wettability and surface free energy of the titanium surfaces; b) the sterilization method changed the electron donor character of the surfaces by changing the amount/nature of physisorbed substances on the surfaces, and c) the chemical composition of the blasting particles did not influence on the electrical charge at physiological pH and the isoelectric point of the surfaces.A second step consisted in the use of a quartz crystal microbalance with monitoring of the energy dissipation to study the adsorption kinetics (amount and conformation) and adsorption competition processes of three proteins of special interest in the healing processes of bone -bovine serum albumin (BSA), fibrinogen (Fbg), and fibronectin (Fn)-on smooth TiO2-coated sensors. Different patterns of adsorption with processes in one, two or multiple distinguishable steps were determined depending of the protein in solution. The BSA adlayers showed the most significant changes in their mechanical properties/conformation/incorporation of water until steady protein-adsorption conditions were reached. BSA, the smallest of the tested proteins, displaced Fn and Fbg when in competition for adsorption, which is an indication of its higher affinity for TiO2 surfaces. Fluorescent labelling techniques where used to study protein adsorption on blasted rough surfaces. Most significantly, the amount of Fn and BSA adsorbed on blasted surfaces was positively correlated with their surface energy. The adsorption of fibronectin from solution on shot-blasted rough titanium surfaces resulted in an irregular pattern of adsorption with a higher amount of protein adsorbed on peaks than on valleys of the topography.Further, the spatial organization of the osteoblast extracellular matrix, ECM, on smooth and rough Ti surfaces was evaluated by visualizing fluorescently-stained Fn-fibrils. Osteoblast-like cells deposited Fn- fibrils in a specific facet-like pattern that was organized within the secreted total matrix. It appeared as a film overlying the top of the different rough titanium surfaces. Interestingly, the thickness of this layer increased with the roughness of the underlying topography, but no more than half of the total maximum peak-to-alley distance was covered.Finally, taking into consideration the differences in ECM organization and Fn adsorption on the tested Ti surfaces a qRT-PCR study was carried out to elucidate the influence of titanium surface properties with and without Fn-precoatings on the osteoblast response. The expression of &#61537;5 integrin subunit gene, as a marker for cell adhesion, was increased in SiC-blasted surfaces compared to alumina-blasted surfaces. This was related to the higher amount of adhesive-protein Fn adsorbed caused by the higher surface energy of SiC-blasted surfaces. The increase of roughness as well as the presence of alumina particles on blasted surfaces increased ALP activity and ALP mRNA gene expression by osteoblasts, and so their differentiation.This research work contribute to increase our knowledge on the interactions taking place at the bio/non-bio interface between different biological components -water, proteins, cells- and materials of clinical relevance, such as rough titanium. Theintertwined effects of the different properties of the synthetic surfaces appear as a challenge to unravel the ultimate causes that determine the fate of cells on synthetic biomaterials.

Interfacial features of polymers are a complex, fascinating topic, and industrially very important. There is clearly a need to understand interactions between polymer layers as they can be used for controlling surface properties, colloidal stability and lubrication. The aim of my Ph.D study was to investigate fundamental phenomena of polymers at interfaces, covering adsorption, interactions between polymer layers and surfactants, surface forces and friction between adsorbed layers. A branched brush layer with high water content was formed on silica surfaces by a diblock copolymer, (METAC)m-b-(PEO45MEMA)n, via physisorption. The adsorption properties were determined using several complementary methods. Interactions between pre-adsorbed branched brush layers and the anionic surfactant SDS were investigated as well. Surface forces and friction between polymer layers in aqueous media were investigated by employing the Atomic Force Microscopy (AFM) colloidal probe technique. Friction forces between the surfaces coated by (METAC)m-b-(PEO45MEMA)n in water are characterized by a low friction coefficient. Further, the layers remain intact under high load and shear, and no destruction of the layer was noted even under the highest pressure employed, about 50 MPa. Interactions between polymer layers formed by a temperature responsive diblock copolymer, PIPOZ60-b-PAMPTMA17 (phase transition temperature of 46.1 °C), was investigated in the temperature interval 25-50 °C by using the AFM colloidal probe technique. Friction between the layers increases with increasing temperature (25-45 °C), while at 50 °C friction was found to be slightly lower than that at 45 °C. We suggest that this is due to decreased energy dissipation caused by PIPOZ chains crystallizing in water above the phase transition temperature. The structure of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers was determined by X-ray reflectometry. Surface forces and friction between DPPC bilayer-coated silica surfaces were measured utilizing the AFM colloidal probe technique. Our study showed that DPPC bilayers are able to provide low friction forces both in the gel (below ≈ 41°C) and in the liquid crystalline state (above ≈ 41°C). However, the load bearing capacity is lower in the gel state. This is attributed to a higher rigidity and lower self-healing capacity of the DPPC bilayer in the gel state. Friction forces in single asperity contact acting between a micro-patterned silicon surface and an AFM tip was measured in air. We found that both nanoscale surface heterogeneities and the µm-sized depressions affect friction forces, and considerable reproducible variations were found along a particular scan line. Nevertheless, Amontons’ first rule described average friction forces reasonably well. Amontons’ third rule and Euler’s rule were found to be less applicable to our system. / <p>QC 20141209</p>

The overall thrust of this project is to gain an insight into a class of surface-tethered cross-linked thin films of poly(N-alkylacrylamides) that display a lower critical solution temperature (LCST).The structure of the alkyl group and the modification of the amide groups determine the LCST and resultant volume-phase transition behavior. The aim of this study involves synthesis and characterization of thin films and to correlate the volume-transition behavior to the structure of the alkyl group. For better understanding the volume-transition behavior, the polymer films are perturbed by the Hofmeister salt series to examine trends between different alkyl groups. While most of the studies have been done with bulk gels, the majority of the applications require the use of gels at surfaces and interfaces. Surface attached polymer networks provide an alternative to bulk gels showing superior response times, thus efficiency. Hence it is significant to understand the impact of confinement on the phase transition behavior of a polymer network. Anchoring a polymer network to a surface produces volume phase transition perpendicular to the substrate. The parallel swelling and collapse of the network is highly restricted due to lateral confinement, thus impacting properties such as structure, mechanical properties, dynamics and permeability of the network. Several studies have been done with poly(N-isopropylacrylamide) anchored to a substrate, which have shown significantly different behavior than unconstrained networks. Notable examples include a gradual as opposed to a sharp volume-phase transition, and significantly less swelling above and below the LCST. These studies only looked at poly(NIPAAm); therefore it remains unknown if these results are universal and will apply to other LCST polymers. Hence, we expanded upon these studies to also investigate a library of different LCST polymers belonging to the category of N-alkylacrylamides. I have synthesized the copolymers comprising of N-alkylacrylamides and methacryloxybenzophenone (MaBP). The benzophenone moiety in MaBP is photoreactive, allowing us to cross-link the copolymers by UV irradiation. Surface attached thin films were fabricated by spin coating the solution of copolymers and cross-linking by UV irradiation. The volume phase transitions of the coatings were studied under the influence of temperature and the salts of the Hofmeister series. Information concerning the state of responsive layers, the precise temperature at which the collapse occurs, and the changes in the molecular environment during the transition were investigated by ellipsometry and ATR-FTIR. In a longer perspective, understanding the transition behavior and the influence of salts governing this transition provides a better understanding of the interactions of biopolymers in natural systems.

Tumour necrosis factor-stimulated gene-6 (TSG-6) is a protein expressed in a wide range of cell types and tissues, predominantly in response to inflammatory stimuli. The expression of TSG-6 is believed to be associated with the protection of tissues from the damaging effects of inflammation. In animal models treatment with TSG-6 protein has been found to reduce inflammatory damage in myocardial infarction, corneal injury and arthritis. Endogenous TSG-6 production has been suggested to play a protective role in inflammatory arthritis and has been implicated in bone homeostasis. The expression of TSG-6 is also essential in the process of cumulus matrix formation that occurs around the oocyte in the periovulatory period and is necessary for successful ovulation and fertilisation. In many cases the mechanism underlying a particular TSG-6 function is not fully understood. TSG-6 has numerous binding partners including the serum glycoprotein inter-alpha-inhibitor (IαI), the growth factor bone morphogenetic protein-2 (BMP-2) and the extracellular matrix protein fibronectin, as well as glycosaminoglycans (GAGs) such as hyaluronan and heparan sulphate (HS). The TSG-6 protein is mostly composed of contiguous Link and CUB domains, with the majority of ligand binding sites identified within the Link module. The CUB domain of TSG-6 has been less extensively studied. Here biophysical techniques have been used to investigate the TSG-6 interactome including both the Link module and CUB domain. Intrinsic fluorescence spectroscopy was used to establish the metal-ion binding properties of the CUB domain, which was established to have a high affinity Ca2+-binding site. Using surface plasmon resonance (SPR), a novel metal-ion dependent interaction was found for the CUB domain of TSG-6 and the heavy chains (HCs) of IαI. Investigation using mutants of both the CUB domain of TSG-6 and HC of IαI established that the metal-ion binding sites within each protein are involved in the interaction. SPR analysis was also used to define the affinities and binding sites for TSG-6 interactions with fibronectin and BMP-2. High affinity interactions between TSG-6 ligands were also revealed (e.g. BMP-2 and HC, fibronectin and HC) and their binding sites defined. The discovery of the novel interactions between these TSG-6 ligands suggests crosstalk within the TSG-6 interactome, with the potential for ternary complex formation or indeed hierarchical orders of binding. Thus work was undertaken to develop a passivated lipid bilayer platform for use with surface sensitive techniques. This platform was used to investigate the hierarchy of protein and GAG interactions using quartz crystal microbalance with dissipation monitoring (QCM-D) and dual polarisation interferometry (DPI). The investigation revealed a novel role for the Link module of TSG-6 in heparin condensation, potentially via protein dimerisation and/or oligomerisation which could affect heparin/HS functions within the extracellular matrix (ECM). Thus the biophysical analysis of TSG-6 presented here has identified novel interactions and functions of TSG-6 which may provide mechanisms for the protective functioning of TSG-6 in inflammation and its ECM structuring role in ovulation.

In-situ chain extension of polymers used in the formulation of artificial tears and mild gelation are techniques to increase the residence time of eye drops on cornea. In-situ chain extension also helps to control the stability of ophthalmic emulsions both in the bottle and in the tear film. In this work, the interaction of hydrophobically modified guar and tear proteins as a method of polymer chain extension and mild gelation has been evaluated. Guar and its derivatives have been found to be very effective for ophthalmic applications. The ideal guar gelation agent is the one that turns on the gelation upon introduction onto the eye and that gelation chemistry is biocompatible and biodegradable. Controllable gelation is desirable to have relatively low viscosity eye drops for easy application and the drops form weak gels in the eye. One recent strategy to cure dry eye disease is to include emulsions in lubricant eye drops. The idea is to supplement the natural lipid layer on the exterior surface of the tear film. Formulating artificial tear emulsions is relatively complicated and must satisfy conflicting criteria. Emulsion droplets should be stable over the period of their shelf life without creaming or aggregate formation. On the other hand, in the tear film the emulsion droplets must cream fast enough and deposit onto the water/lipid film interface on the exterior surface of the tear film. Thus, the emulsion must be stable but not too stable. Initially, science-based design rules were proposed for the development of future generations of lubricant eye drops. The effect of guar molecular weight and concentration on emulsion stability was evaluated. According to the concentration-molecular weight plot, polymer solutions can be divided into stable and unstable regions. They are defined based on the critical flocculation concentration (CFC) and critical viscosity concentration (C*). Inverted QCM-D has been proposed as a simple and fast method to define the stability of oil in water emulsion systems. This technique is a promising alternative for time consuming conventional creaming experiments. Low molecular weight guar can be optimized to out-perform high molecular weight guars without the complications of formulating eye drops with high molecular weight polymers. Hydroxypropyl guar samples were oxidized and modified with linear alkyl amines to give a series of hydrophobically modified guars (MGuars). Lysozyme and human serum albumin (HSA), natural tear proteins, are able to extend the effective chain length of MGuar through polymer/protein complex formation. Hydrophobic modifications on guar enable efficient interaction with proteins, through their mutual hydrophobic characteristics. The interaction of proteins with various alkyl chain lengths, degrees of substitution and a range of molecular weights were examined. Binding and rheological measurements were employed to evaluate the interactions efficiency. Our results suggest that higher degrees of substitution and longer alkyl chain length give higher viscosity values. Lowering molecular weight allows for higher concentration, while keeping the initial viscosity constant. Higher viscosity was achieved as the chain extension occurred. The influence of hydrophobic modification and molecular weight variation on lubrication behavior of MGuars has also been determined. Hydrophobic modification enhanced the lubrication between hydrophobic surfaces. However, saturation of hydrophobes with protein abolished the lubricity. / Thesis / Doctor of Philosophy (PhD)

The main objective of this thesis work was to gain understanding of the layer properties and polymer structures that were able to aid lubrication in aqueous media. To this end, three types of polyelectrolytes: a diblock copolymer, a train-of-brushes and two brush-with-anchor mucins have been utilized. Their lubrication ability in the boundary lubrication regime has been examined by Atomic Force Microscopy with colloidal probe. The interfacial behavior of the thermoresponsive diblock copolymer, PIPOZ60-b-PAMPTAM17,on silica was studied in the temperature interval 25-50 ˚C. The main finding is that adsorption hysteresis, due to the presence of trapped states, is important when the adsorbed layers are in contact with a dilute polymer solution. The importance of trapped states was also demonstrated in the measured friction forces, where significantly lower friction forces, at a given temperature, were encountered on cooling than on the preceding heating stage, which was attributed to increased adsorbed amount. On the heating stage the friction force decreased with increasing temperature despite the worsening of the solvent condition, and the opposite trend was observed when using pre-adsorbed layers (constant adsorbed amount) as a consequence of increased segment-segment attraction. The second part of the studies was devoted to the interfacial properties of mucins on PMMA. The strong affinity provided by the anchoring group of C-PSLex and C-P55 together with their more extended layer structure contribute to the superior lubrication of PMMA compared to BSM up to pressures of 8-9 MPa. This is a result of minor bridging and lateral motion of molecules along the surface during shearing. We further studied the influence of glycosylation on interfacial properties of mucin by utilizing the highly purified mucins, C-P55 and C-PSLex. Our data suggest that the longer and more branched carbohydrate side chains on C-PSLex provide lower interpenetration and better hydration lubrication at low loads compared to the shorter carbohydrate chains on C-P55. However, the longer carbohydrates appear to counteract disentanglement less efficiently, giving rise to a higher friction force at high loads. / <p>QC 20170407</p>

The cellular response to a biomaterial, such as a dental implant, is mainly governed by the surface properties, and can thus be altered by the introduction of a surface coating. In this thesis the buildup of a biomacromolecule-based coating formed by layerby-layer (LbL) deposition of the charged polypeptides poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA) has been studied. In an attempt to make these coatings bioactive and useful for bone-anchored implants, an amelogenin protein mixture (EMD), has been immobilized in these thin polyelectrolyte multilayer (PEM) films. Multilayers were also built by LbL deposition of the natural biomacromolecules collagen (Col) and hyaluronic acid (HA). Multilayer films of these two extra-cellular biomacromolecules should be of interest for use as a scaffold for tissue engineering. The buildup of the multilayer films has been followed in situ, using ellipsometry, quartz crystal microbalance with dissipation (QCM-D), and dual polarization interferometry (DPI). The studied PLL/PGA multilayers were found to be highly hydrated, and to exhibit a two-regime buildup behavior, with an initial “slow-growing” regime, and a second “fast-growing” regime with a linear growth in film thickness and more than linear growth in mass. A net diffusion of polypeptides into the film during the buildup led to an increase in density of the films for each layer adsorbed. A change in density was also observed in the Col/HA film, where HA penetrated and diffused into the porous fibrous Col network. The formed PLL/PGA films were further found to be rather stable during drying, and post-buildup changes in temperature and pH, not losing any mass as long as the temperature was not raised too rapidly. The film thickness responded to changes in the ambient media and collapsed reversibly when dried. A swelling/de-swelling behavior of the film was also observed for changes in the temperature and pH. The EMD protein adsorbed to silica surfaces as nanospheres, and could by itself form multilayers. The adsorption of EMD onto PLL/PGA multilayer films increased at lower pH (5.0), and EMD could be immobilized in several layers by alternate deposition of EMD and PGA. / QC 20101019